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Molecular design of luminescent organic-inorganic hybrid materials activated by europium (III) ions
Institution:1. International MegaGauss Science Laboratory (IMGSL), Institute for Solid State Physics, University of Tokyo, Chiba, Japan;2. Laser and Synchrotron Research Center (LASOR), Institute for Solid State Physics, University of Tokyo, Chiba, Japan;3. Graduate School of Frontier Bioscience, Osaka University, Osaka, Japan;4. Department of Natural Science, Ibaraki National College of Technology, Ibaraki, Japan;1. V.N. Karazin Kharkiv National University, Faculty of Chemistry, 61022 Kharkiv, Ukraine;2. Institute of Chemistry, Jan Kochanowski University, 25-406 Kielce, Poland;3. P.J. Safarik University in Kosice, Institute of Physics, 041 54 Kosice, Slovakia;4. Regional Centre of Advanced Technologies and Materials, 771 46 Olomouc, Czech Republic;5. Institute of Pharmacy, Martin-Luther University Halle-Wittenberg, 06120 Halle (Saale), Germany;6. P.J. Safarik University in Kosice, Institute of Chemistry, 041 54 Kosice, Slovakia
Abstract:Luminescent hybrid materials consisting in rare-earth (Eu3+, Gd3+) organic complexes covalently attached to a silica-based network have been obtained by a sol–gel process. Four dicarboxylic acids with different aromatic subunits (dipicolinic acid, 4-phenyl-2,6-pyridinedicarboxylic acid, 4-(phenylethynyl)-2,6-pyridinedicarboxylic acid and 2,6-Bis(3-carboxy-1-pyrazolyl)pyridine) have been chosen as ligands for Ln3+ ions. They were grafted to 3-aminopropyltriethoxysilane (APTES) to give organically modified alkoxysilanes that were used as molecular precursors for the preparation of hybrid materials. Ln3+ first coordination sphere, composition of the siloxane matrix and connection between the organic and inorganic parts have been characterized by infrared spectroscopy, by 13C29Si solid-state NMR as well as by elemental analyses. UV excitation in the organic component resulted in strong emission from Eu3+ ions due to an efficient ligand-to-metal energy transfer. As compared to reference organic molecules, hybrid samples exhibited similar emission properties under UV excitation in addition to mainly unchanged excited states lifetimes. However, by direct excitation of the Eu3+-5D0 energy level, the presence of two different site distributions were evidenced in the four hybrid compounds. Emission features related to each of these site distributions and their respective attribution were investigated. Variations in the relative emission intensities were observed according to the nature of the organic chromophore. These variations were discussed in relation to the ATE (Absorption-Transfer-Emission) mechanism and to the relative energy positions of the ligand and the rare-earth ions respectively.
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